Optical transmission system including a plurality of optical transmission devices

ABSTRACT

Two multiplexing/demultiplexing sections of working and protection sides are prepared for each of a plurality of optical transmission devices which constitute a system, and the optical transmission devices are synchronized with each other to execute switching between the working and protection sides so that one of the working and protection sides can be selected for the entire system. Each expansion device collects optical line trouble information for each of the working and protection sides, and transmits to a main device. The main device integrates the information with trouble information transmitted from expansion devices per expansion device. The main device converts the integrated trouble information into point information, totals for each of the working and protection sides, compares, and decides which of the working and protection sides is to be selected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical transmission systemincluding a plurality of optical transmission devices.

2. Description of the Related Art

Recently, regarding an optical transmission device, to achieve a highcapacity of optical transmission, an optical transmission systemoperated by combining some basic optical transmission devices has beenconstructed. In such an optical transmission system constructed bycombining a plurality of optical transmission devices (also calledShelves), when each optical transmission device is provided withinformation including a log-in ID for optical transmission devicemanagement, and when the information is managed for each opticaltransmission device, a system operation becomes complex. Accordingly,there is a strong demand for a system which enables an easier operationby managing an optical transmission system including a plurality ofoptical transmission devices as a single device, and reducing networkresources.

FIG. 14 is a diagram showing a functional constitution in an opticaltransmission system (referred to as “conventional device”) whichincludes one basic optical transmission device. As shown in FIG. 14, theconventional device is arranged on a transmission line of opticalsignals. The conventional device includes a plurality of opticalinterface units (INF) 15 for receiving/transmitting optical signalsfrom/to the other devices, and multiplexer/demultiplexer sections(referred to as MUX/DMUX sections, hereinafter) 12, 13 formultiplexing/demultiplexing the signals received by each of theinterface units 15, and outputting to the interface units 15corresponding to addresses of the signals. Each of the MUX/DMUX sections12, 13 includes a signal connection converting section (crossconnection) 12 a for connecting an input signal to an outgoing pathcorresponding to its address.

Thus, two communication units (Units) which include the MUX/DMUXsections are disposed in the optical transmission device. One of the twoMUX/DMUX sections 12, 13 is used as a working side (working line (WK))device, and the other is used as a protection side (protection line(PT)) device used when the working side fails. Accordingly, the signaltransmission line is made redundant. A state of the optical transmissiondevice is monitored by a state monitoring section, and switching betweenthe WK side and the PT side is carried out by a switching managingsection.

There is a limit to the number of slots for connection to one basicoptical transmission device, i.e., the number of optical interface units15 mounted on one basic transmission device. Thus, to realizelarge-capacity transmission, an optical transmission system in which aplurality of basic optical transmission devices are interconnected mustbe constructed. To realize such a configuration, cooperation isnecessary among the plurality of interconnected optical transmissiondevices in terms of signal connection. Accordingly, cooperation mayconceivably be established among the optical transmission devices interms of the signal connection by using parts of the optical interfaceunits 15 to execute transfer of signals among the optical transmissiondevices.

However, when a capacity of the interface unit is used to connect eachoptical transmission device, a transmission permission amount of thedevice is consequently reduced by a connection amount with the othertransmission device. Besides, presence of the signal connectionconverting section in each optical transmission device necessitatescomplex signal connection management.

Thus, in the configuration in which the plurality of opticaltransmission devices are connected, a functional constitution as shownin FIG. 15 is conceivable. FIG. 15 shows a functional constitution inthe configuration in which the plurality of optical transmission devicesare interconnected. According to the constitution, classification isemployed in which one of the plurality of optical transmission devicesbecomes a main device (MAIN Shelf) 11, while the other opticaltransmission devices become expansion devices (Expansion (EXP) Shelves)21. The signal connection converting section 12 a is disposed in WK andPT MUX/DMUX sections 12, 13 alone mounted on the main device.

Accordingly, it is possible to concentrate management regarding complexsignal connection conversion on the main device. Inter-opticaltransmission device connecting functions are provided to the WK and PTMUX/DMUX sections 12, 13 disposed in each optical transmission device,whereby signal connection conversion is enabled among the opticaltransmission devices, and information can be transferred between statemonitoring sections 17 a, 27 a and between switching managing sections171 b, 271 b of each optical transmission device.

According to the constitution, switching states (selecting states) ofthe WK/PT sides must be the same between the optical transmissiondevices. That is, when the WK MUX/DMUX section 12 is made active in themain device, the WK MUX/DMUX section 12 is similarly made active in theexpansion device. Conversely, when the PT MUX/DMUX section 13 is used inthe main device, the PT MUX/DMUX section 13 is similarly used in theexpansion device. Otherwise, a signal phase difference is generatedbetween the main device and the expansion device to cut off signals.Therefore, a switching operation of the communication unit whichincludes the MUX/DMUX sections 12, 13 must be executed insynchronization between the optical transmission devices.

Normally, the switching of the communication unit which includes theMUX/DMUX sections is controlled based on troubles of the unit such as afailure of the communication unit itself, unit omission, or a powersupply trouble. However, in the functional constitution shown in FIG.15, since the MUX/DMUX sections 12, 13 handle an optical line totransfer signals among the optical transmission devices, a trouble ofthe optical line must also be a cause of unit switching.

The signal to interconnect the optical transmission devices needs tohave a signal capacity of about 100 gigabytes to realize a largecapacity. Thus, many optical fibers are used to make connection.Accordingly, to set the trouble of the optical line as a cause of unitswitching, line trouble states of the lines are collected by the opticaltransmission devices, and trouble information are combined for theentire system. A switching state that can save as many lines as possiblemust be determined from the huge amount of trouble information, and unitswitching must be executed within a short time.

However, to manage a huge amount of trouble patterns and to decide aswitching state which matches each trouble occurrence state, complexdetermination must be made, and much time must be expended fordetermination as to execution of switching. Accordingly, a case mayoccur in which standard switching regulations of 50 milliseconds by asingle trouble and 100 milliseconds or less by a plurality of troublescannot be met. A huge amount of test patterns must be implemented totest all the cases for the huge amount of trouble patterns, and muchtime must be expended to guarantee qualities. In addition, presence ofthe huge amount of trouble patterns makes difficult determination as towhether test patterns corresponding to all the trouble patterns areincluded or not, and establishment of a testing range. Therefore, it isdifficult to secure a quality of the optical transmission system.

Note that conventional art documents concerning the present inventionare as follows. The conventional art documents are “Japanese PatentApplication No. 07-240732 A”, “Japanese Patent Application No.2003-304274 A”, “Japanese Patent Application No. 03432958 B”, and“Japanese Patent Application No. 02570016 B”.

SUMMARY OF THE INVENTION

The present invention has an object to realize proper switching within ashort time by simplifying switching determination between working andprotection sides.

The present invention employs the following constitution to solve theaforementioned problems. That is, the present invention provides anoptical transmission system which haves a plurality of opticaltransmission devices including one main device and a plurality ofexpansion devices. The optical transmission device comprises a pluralityof interface units which control signal transmission/reception, and eachmultiplexing/demultiplexing section of each of working and protectionsides which multiplexes/demultiplexes a signal transmitted/received byeach interface unit. The multiplexing/demultiplexing section of theworking side of each expansion device is connected through a pluralityof optical lines to the multiplexing/demultiplexing section of theworking side of the main device. The multiplexing/demultiplexing sectionof the protection side of each expansion device is connected through aplurality of optical lines to the multiplexing/demultiplexing section ofthe protection side of the main device. The multiplexing/demultiplexingsection of each of the working and protection sides of the main devicecomprises a switching section which switches an output destination of asignal input to each of the main device and the expansion devicesaccording to an address of the signal. Each of the plurality ofexpansion devices comprises a expansion device side trouble informationcollecting section which collects trouble information, indicating atrouble state of one or more optical lines among the plurality ofoptical lines for receiving a signal from the main device, for each ofthe working and protection sides, a transmitting section which transmitsthe collected trouble information of the working and protection sides tothe main device, and a expansion device side working/protectionswitching control section which controls switching between the workingand protection sides according to a switching instruction between theworking and protection sides received from the main device. The maindevice comprises a main device side trouble information collectingsection which collects trouble information indicating a trouble stateof, among the plurality of optical lines for connecting the main deviceand the expansion devices, the optical line for receiving a signal fromeach of the expansion devices for each of the working and protectionsides and each expansion device, a receiving section which receives thetrouble information of the working and protection sides collected by theexpansion device side trouble information collecting section from theexpansion device, an integrating section which creates integratedtrouble information integrating the trouble information collected by themain device side trouble information collecting section and the troubleinformation collected by the expansion device side trouble informationcollecting section for each of the working and protection sides and eachexpansion device, a storing section which stores point informationcorresponding to the integrated trouble information, a convertingsection which converts the integrated trouble information into the pointinformation stored in the storing section, a totaling section whichtotals converted point information regarding each of the working andprotection sides, a deciding section which decides which of the workingand protection sides is selected by comparing the totaled pointinformation with each other, and a main device side working/protectionswitching control section which controls switching between the workingand protection sides for the main device according to a deciding resultof the deciding section, and notifies each expansion device of aswitching instruction similar to that for the main device.

According to the present invention, the two multiplexing/demultiplexingsections of the working and protection sides are prepared for each ofthe plurality of optical transmission devices which constitute thesystem, and the optical transmission devices are synchronized with eachother to execute switching between the working and protection sides sothat one of the working and protection sides can be selected for theentire system.

To decide such switching between the working and protection sides, eachexpansion device collects trouble information of, among the plurality ofoptical lines for connecting the main device, one or more optical linesfor receiving the signal from the main device for each of the workingand protection sides, and transmits to the main device.

The main device collects trouble information of, among the plurality ofoptical lines for connecting the main device and the expansion device,the optical line for transmitting the signal from each expansion deviceto the main device for each of the working and protection sides, andintegrates the trouble information and the trouble informationtransmitted from the expansion devices on the basis of per expansiondevice. Then, the main device converts each of the integrated troubleinformation into point information, and totals such point informationfor each of the working and protection sides. Subsequently, the maindevice compares the totaled point information to decide which of theworking and protection sides is to be selected, and executes switchingbetween the working and protection sides of the main device and theexpansion devices according to the result.

Thus, according to the present invention, switching determination isfacilitated by integrating the point information indicating a state ofexecuting switching between working and protection sides. As a result,since determining processing necessary for switching judgment is greatlyreduced, it is possible to shorten a time necessary for switchingdetermination, and to shorten a time necessary for switching processing.

According to the present invention, the point information is a numericalvalue allocated according to a degree of a trouble indicated by theintegrated trouble information so that the deciding section selects sideof a good degree of a trouble between the working and protection sides.

According to the present invention, to make switching determinationbetween the working and protection sides, the main device converts theintegrated trouble information into the point information, i.e., thenumerical value allocated according to a degree of trouble, and comparessuch numerical values to lastly decide switching.

Thus, according to the present invention, in the switching determinationbetween the working and protection sides, it is possible to select aside which can pass a signal even a little only by comparing thenumerical values (point information).

In addition, according to the present invention, the main device sideworking/protection switching control section notifies each expansiondevice of the switching instruction by using an overhead portion of anoptical communication frame transmitted through at least one of theplurality of optical lines for connecting themultiplexing/demultiplexing section of the protection side of the maindevice and the multiplexing/demultiplexing section of the protectionside of each expansion device.

According to the present invention, to transmit the above switchinginstruction, the overhead portion of the optical communication framedefined according to an optical communication standard is used.

Thus, according to the present invention, it is possible to increase ause rate of software resources for optical communication.

According to the present invention, if the switching instruction fromthe main device cannot be received when a current switched sate is aprotection side, the expansion device side working/protection switchingcontrol section controls switching of the own device to the workingside.

According to the present invention, when it is detected that eachexpansion device cannot receive the switching instruction to be receivedfrom the main device due to a line trouble, the own device is switchedto the working side.

Thus, according to the present invention, even when each expansiondevice cannot receive the switching instruction from the main device,unified switching between the working and protection sides in the entiresystem is enabled, and redundancy can be achieved for the system.

According to the present invention, if all the degrees of troubles ofthe plurality of optical lines for both the working and protection sidesin one of the plurality of expansion devices are not good, theintegrating section excludes the trouble information of the expansiondevice from an integration target.

According to the present invention, when the trouble information of,among the plurality of optical lines for connecting the main device andthe expansion devices, the optical line for transmitting a signal fromthe expansion devices to the main device are collected for each of theworking and protection sides, if it is determined based on the collectedtrouble information that all the degrees of troubles of the plurality ofoptical lines in both the working and protection sides of the pluralityof expansion devices are not good, the main device excludes the troubleinformation of the expansion devices from integration target.

Thus, according to the present invention, with priority given to arelation with a normal device among the expansion devices, it ispossible to make switching determination in the entire system, and toachieve redundancy of the system.

According to the present invention, it is possible to realize properswitching within a short time by facilitating determination of switchingbetween the working and protection sides.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing connection among optical transmissiondevices;

FIG. 2 (FIGS. 2A and 2B) is a diagram showing trouble informationcollection in the optical transmission devices;

FIG. 3 is a diagram showing trouble information integration in a maindevice;

FIG. 4 is a diagram showing a trouble information type and troublepriority;

FIG. 5 is a diagram showing an H/W concept in a plurality of opticaltransmission devices according to an embodiment of the presentinvention;

FIG. 6 (FIGS. 6A, 6B, and 6C) is a diagram showing a functionalconstitution in the plurality of optical transmission devices accordingto the embodiment of an optical transmission system of the presentinvention;

FIGS. 7A and 7B are diagrams showing a K1/K2 byte using method;

FIG. 8 is a diagram showing a trouble point conversion table;

FIG. 9 is a diagram showing a functional constitution of a switchingmanaging section;

FIG. 10 is a flowchart showing an operation flow of a switching managingsection of a expansion device;

FIG. 11 (FIGS. 11A and 11B) is a flowchart showing an operation flow ofa switching managing section of a main device;

FIG. 12 (FIGS. 12A and 12B) is a flowchart showing an operation flow ofthe switching managing section of the expansion device whencommunication with the main device is cut off;

FIG. 13 is a diagram showing a processing flow of the switching managingsection of the main device when the expansion deice is not subjected toswitching determination;

FIG. 14 is a diagram showing a functional constitution in a conventionaldevice configuration; and,

FIG. 15 is a diagram showing a functional constitution in aconfiguration of a plurality of optical transmission devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

<Outline of Embodiment of the Invention>

To explain an embodiment of the present invention, an outline thereofwill first be given. FIG. 1 is an explanatory diagram of an outline ofan optical transmission system according to this embodiment of thepresent invention. FIG. 1 shows inter-optical transmission deviceconnection in which a main device and two expansion devices constitutingthe optical transmission system are interconnected. The main devicecorresponds to a main device of the present invention, and the expansiondevices correspond to expansion devices of the present invention. Themain device 11 and the expansion devices 21 and 31 are interconnectedthrough a plurality of optical fibers 41. Each of the opticaltransmission devices 11, 21, and 31 includes two communication unitswhich include multiplexer/demultiplexer sections (MUX/DMUX sections).One of the two communication units is used as a working (WK)communication unit, and the other is used as a protection (PT)communication unit. The multiplexer/demultiplexer section (MUX/DMUXsection) corresponds to a multiplexer/demultiplexer section of thepresent invention.

The WK communication units (communication units #3 and #5) of theexpansion devices 21 and 31 are connected through the optical fibers 41to the WK communication unit (communication unit #1) of the main device11. Similarly, the PT communication units (communication units #4 and#6) of the expansion devices 21 and 31 are connected through the opticalfibers 41 to the PT communication unit (communication unit #2) of themain device 11.

According to this embodiment, each of the optical transmission devicescollects trouble information. Next, description will be made of howtrouble information regarding each of the optical transmission devicesare collected in a connection constitution of the optical transmissiondevices shown in FIG. 1. FIG. 2 is a diagram showing an outline ofcollection of trouble information by each of the optical transmissiondevices. The trouble information is information regarding troubles whichneed unit switching (switching between the WK and PT sides), and thereare troubles of the unit system such as a failure of a unit itself(board or the like), unit omission, and a power supply trouble, and linetroubles such as optical signal degradation.

To begin with, in the expansion devices 21 and 31, regarding the WK andPT communication units, line troubles of sides in which thecommunication units receive signals, and unit troubles of thecommunication units are individually collected.

For example, in an example shown in FIG. 2, for the WK communicationunit #3 of the expansion device 21, a line trouble concerning a line forreceiving an optical signal from the WK communication unit #1 of themain device 11, and a unit trouble of the communication unit #3 arecollected. In addition, for the PT communication unit #4 of theexpansion device 21, a line trouble concerning a line for receiving theoptical signal from the communication unit #1, and a unit trouble of thecommunication unit #4 are collected, and the collected troubleinformation are integrated.

In the expansion device 31, as in the case of the expansion device 21,line troubles and unit troubles are collected for the WK communicationunit #5 and the PT communication unit #6, and the collected troubleinformation are integrated.

On the other hand, in the main device 11, for the WK and PTcommunication units #1 and #2, by a method similar to that of each ofthe expansion devices 21 and 31, trouble information regarding line andunit troubles are collected, and integrated. That is, for thecommunication unit #1 of the main device 11, a line trouble concerning aline for receiving an optical signal from the communication unit #3 ofthe expansion device 21, and a unit trouble of the communication unit #1are collected, and integrated. A line trouble regarding a line throughwhich the communication unit #1 receives an optical signal from thecommunication unit #5 of the expansion device 31, and the unit troubleof the communication unit #1 are collected, and integrated. In addition,for the PT communication unit #2 of the main device 11, collection andintegration processing similar to that of the trouble informationregarding the communication unit #1 is carried out.

The integrated trouble information are represented by states of, e.g.,“(X)-F”, “(X)-D” and the like. The “(X)” is identification informationof a communication unit. For example, if a communication unit is the WKcommunication unit #3 of the expansion device 21, “(X)” is “(3)”. The“F” is a state of a signal failure (fail), and the “(D)” is a state ofsignal degradation (degrade).

Note that, in the examples shown in FIGS. 1 and 2, the communicationunits are interconnected through three optical tape fibers whichconstitute the optical fiber 41, and trouble information are integratedfor each optical tape fiber. The trouble information integrated for eachcommunication unit is referred to as first integrated information. Forexample, for the communication unit #3, the first integrated informationis “(3)-F” and “(3)-D” for each optical tape fiber.

The main device 11 collects the trouble information collected andintegrated for each communication unit of the optical transmissiondevice, and integrates for each of the WK and PT sides. Next,description will be made of how the first integrated informationobtained as described above for each communication unit of the opticaltransmission device is further integrated as a system. FIG. 3 is adiagram showing an outline of integration of trouble information in themain device. The first integrated information collected in the expansiondevices 21 and 31 shown in FIG. 2 is notified to the main device 11through the optical line for connecting the optical transmissiondevices.

In the main device 11, second integrated information that integrates thefirst integrated information is created for each of the WK and PTcommunication units, and each communication unit of the expansion deviceside connected to the communication unit. That is, for the WKcommunication unit #1 of the main device 11, second integratedinformation 49 a that integrates first integrated information 24 a ofthe communication unit #3 notified from the expansion device 21 andfirst integrated information 14 a concerning the communication unit #3of the communication unit #1 is created. Similarly, second integratedinformation 49 c that integrates first integrated information 34 a ofthe communication unit #5 notified from the expansion device 31 andfirst integrated information 14 c concerning the communication unit #5of the communication unit #1 is created.

For the PT communication unit #2 of the main device 11, secondintegrated information 49 b that integrates first integrated information24 b of the communication unit #4 notified from the expansion device 21and first integrated information 14 b concerning the communication unit#4 of the communication unit #2 is created. Similarly, second integratedinformation 49 d that integrates first integrated information 34 b of acommunication unit #6 notified from the expansion device 31 and firstintegrated information 14 d concerning the communication unit #6 of thecommunication unit #2 is created.

Subsequently, in the main device 11, each second integrated informationis converted into a predetermined trouble point. Trouble points aretotaled in the WK and PT sides, and results of the totaling are comparedwith each other. If a result of the comparison is that a trouble pointof one side currently in an active state is smaller than that of theother side, a selected state of the side is maintained. On the otherhand, if a trouble point of one side currently in the active state islarger than that of the other side, a switching operation of the side ofthe active state is executed.

That is, for example, when the WK side is in an active state and the PTside is in a standby state, if a trouble point of the WK side is smallerthan that of the PT side, the active state of the WK side is maintained.On the other hand, if the trouble point of the WK side is larger thanthat of the PT side, the WK side is switched to a standby state, and thePT side is switched to an active state. In other words, the side of theactive state is switched from the WK side to the PT side. By such simpledetermination processing, i.e., large and small comparison of troublepoints, switching determination processing is carried out between the WKand PT sides in the entire optical transmission system.

The switching processing is executed by giving a switching statenotification from the main device 11 to each of the expansion devices 21and 31. Each of the expansion devices 21 and 31 is constituted toforcibly switch the WK side (working side) to an active state when theswitching state notification cannot be received from the main device 11because of a line trouble or the like. Accordingly, it is possible tomaintain a unified switching state as the optical transmission system.

Next, referring to FIG. 4, description will be made of trouble prioritywhich becomes an important indicator to decide a trouble point in theconversion of the trouble information into the trouble point. FIG. 4 isa diagram showing a trouble information type and the trouble priority.The trouble priority is a value indicating seriousness of a trouble. Ahigher priority value means a more serious trouble situation. A value ofeach trouble point is set to be larger as the trouble priority ishigher.

In an example shown in FIG. 4, in order of high priority, a trouble ofeach communication unit (UNIT), a line trouble (SF: signal failure), aline trouble (SD: signal degradation), a Manual switching request, andNR (no request: no alarm) are set. The priority are positioned in orderof troubles being obstacles to signal transmission.

First, a trouble of the communication unit (UNIT) of the Protect side ishighest in the trouble priority. In other words, This is positioned as amost serious trouble. According to this embodiment, as described above,it is because the notification of the first integrated information fromeach of the expansion devices 21 and 31 to the main device 11, and thenotification of the switching state from the main device 11 to each ofthe expansion devices 21 and 31 are carried out through the optical linefor connecting the communication units of the Protect side, andsynchronization cannot be set among the communication units of theentire system if the information cannot be transferred among the opticaltransmission devices. Thus, the trouble is positioned as the mostserious trouble. Next, a trouble of the communication unit of the Workside is positioned.

Regarding information of line troubles, the number of optical lines forconnecting the optical transmission devices is indicated by n, andhigher priority is set in order of larger numbers of lines, i.e., inorder of the larger number of lines in which troubles occur. For SF-n,the line trouble of the Protect side is higher in priority than that ofthe Work side. As in the aforementioned case, it is because the firstintegrated information and the second integrated information aretransferred between the optical transmission devices through the linefor connecting the communication units of the Protect side.

The trouble priority shown in FIG. 4 is used when the expansion devices21 and 31 notify the first integrated information 24 a, 24 b, 34 a, and34 b to the main device 11. For example, it is assumed that thecommunication unit #3 of the expansion device 21 of FIG. 2 detects (3)-Fthrough a first line and a second line of the optical fiber 41, and(3)-D through a third line. In this case, the expansion device 21determines that SF-2 and SD-1 have been generated in the communicationunit #3. Here, the expansion device 21 determines that the SF-2 (Work)is higher in priority than the SD-1 (Work) by using the trouble priorityshown in FIG. 4, and notifies the main device 11 that integratedinformation of the communication unit #3 is the SF-2. Then, the maindevice 11 creates second integrated information 49 a to 49 d by usingthe integrated information notified from the expansion devices 21 and31.

Embodiment

Next, the embodiment of the present invention will be described. Theconstitution of the embodiment is illustrative but not limitative of theconstitution of the present invention.

<<Device Constitution>>

FIG. 5 is a diagram showing a hardware (H/W) concept according to theembodiment of the optical transmission system of the present invention.Hereinafter, referring to FIG. 6, the H/W concept constitution of theembodiment of the present invention will be described.

The optical transmission system includes a plurality of opticaltransmission devices, and the plurality of optical transmission devicesinclude a main device and a plurality of expansion devices connected tothe main device. FIG. 5 shows one main device 110, and expansion devices210, 310 connected through optical fibers 41 to the main device 110.However, the number of expansion devices connected to the main devicemay be two or more.

<<<Main Device>>>

An H/W constitution of the main device 110 will be described. In FIG. 5,the main device 110 includes a plurality of interface units (INF units)15, two communication units (STS-SF) 16 a, 16 b, two TCA units 29 a, 29b, and a CPU unit 17.

Each INF unit 15 is composed of an optical interface unit (interfacecard). The INF unit 15 is connected to the other device through anoptical line drawn from the optical interface unit, and has a functionof terminating each signal. Note that, the INF units 15 can be mountedup to 20 one optical transmission device.

Each of the communication units 16 a and 16 b includes amultiplexer/demultiplexer for multiplexing/demultiplexing a signalreceived by each INF unit 15, and a crossconnecting function ofswitching an output destination of the signal according to its address.One of the communication units (communication unit 16 a here) is used asa communication unit of a WK side (working side), and the other(communication unit 16 b) is used as a PT side (protection side). Unitswitching means switching of a communication unit of an active statebetween the communication units 16 a and 16 b. By the unit switching,the side of the active state is switched between the WK and PT sides.

TCA units 19 a and 19 b generate clock signals to synchronize the signalreceived by each INF unit 15 between networks. The TCA units 19 a and 19b are disposed for each of the communication units 16 a and 16 b, andgenerate clock signals for each of the communication units.

The CPU unit 17 includes a CPU (Central Processing Unit), a memory, anI/O interface, and the like. The CPU executes a program stored in thememory to control operations of the INF units 15 and the communicationunits 16 a and 16 b, and manages information thereby obtained en bloc.In addition, the CPU unit 17 controls transfer of signals with theexpansion devices 210 and 310 through the communication units 16 a and16 b.

<<<Expansion Device>>>

The expansion devices 210 and 310 are similar in constitution to eachother. The expansion devices 210 and 310 are similar in constitution tothe main device 110. However, communication units 26 a, 26 b, and thecommunication units 36 a, 36 b of the expansion devices 210 and 310 haveno crossconnecting functions. This point is different from the maindevice 110. It is because by mounting the crossconnecting function onthe main device 110 alone and executing the signal connection managementin the main device 110 alone, complex management of signal connectionconversion is unified and simplified.

<<<Connection Constitution>>>

The communication unit 16 a of the main device 110 is connected throughan optical fiber 410 a to the communication unit 26 a of the expansiondevice 210, and through an optical fiber 410 c to the communication unit36 a of the expansion device 310. In addition, the communication unit 16b of the main device 110 is connected through an optical fiber 410 b tothe communication unit 26 b of the expansion device 210, and through anoptical fiber 410 d to the communication unit 36 b of the expansiondevice 310.

Each of the optical fibers 410 a, 410 b, 410 c, and 410 d is composed ofthree optical tape fibers. In one optical tape fiber,transmission/reception of optical signals through 12 lines is realized.In addition, by using an overhead portion of one optical line in oneoptical tape fiber for connecting the communication units of the PTside, switching between the WK and PT sides, i.e., transfer ofinformation for unit switching, is executed.

<<Functional Constitution of Device>>

Next, description will be made of a functional constitution in thedevice shown in FIG. 5. FIG. 6 is a diagram showing a functional blockof the optical transmission system shown in FIG. 5. Reference numeralsof FIG. 6 are denoted by similar reference numerals for similar portionsin correspondence to the H/W concept constitution of FIG. 5.

In FIG. 6, the main device 110 includes a plurality of interface units(INF) 15 for transmitting/receiving an optical signal with the otherdevice, MUX/DMUX sections 120 and 130 to which each INF 15 is connected,a state monitoring section 17 a, and a switching managing section 17 b.The MUX/DMUX section 120 includes a signal connection converting section121 for realizing a crossconnecting function, a receiving section 122and a transmitting section 123 to which the optical fiber 410 a isconnected, and a receiving section 124 and a transmitting section 125 towhich the optical fiber 410 c is connected. The MUX/DMUX section 130includes a signal connection converting section 131 (not shown) forrealizing a crossconnecting function, receiving sections 132 and 133(not shown) to which the optical fiber 410 b is connected, and areceiving section 134 and a transmitting section 135 to which theoptical fiber 410 d is connected. Note that, the signal connectionconverting section 121 corresponds to a switching section of the presentinvention.

Expansion devices 210 and 310 are similar in constitution. The expansiondevice 210 (310) includes a plurality of INF units 15, MUX/DMUX sections220 and 230 (320 and 330) to which each of the plurality of INF units 15is connected, a state monitoring section 27 a (37 a), and a switchingmanaging section 27 b (37 b).

According to the optical transmission system of this embodiment, thesignal connection converting sections 121 and 131 are disposed in theMUX/DMUX sections 120 and 130 alone of the main device 110, signalsreceived by the main device 110 and the expansion devices 210 and 310are input to the MUX/DMUX sections 120 and 130 of the main device 110,and signal connection is concentratedly executed by the signalconnection converting sections 121 and 131. Accordingly, the signalconnection can be unified management by the main device 110.

Moreover, according to the optical transmission system of thisembodiment, the two communication units are disposed in each opticaltransmission device. The redundant constitution is employed in which oneof the communication unit becomes a WK side, the other becomes a PT sideand, by switching, one of the WK and PT sides is set in an active statewhile the other is set in a standby state. The side of the WK and PTsides that can provide a good signal transmission state is set in anactive state.

Selection of the active state side is carried out as follows accordingto this embodiment. The signal received by each INF 15 is input to thecommunication unit (MUX/DMUX section) of each of the WK and PT sides.Each communication unit (MUX/DMUX section) processes the input signal,and outputs the signal to the INF 15 of the signal transmission side.

Each INF 15 is constituted to receive a signal from the communicationunit (MUX/DMUX section) of each of the WK and PT sides. The INF 15includes a selector for selecting one of the signals received from thecommunication units. The signal of the side selected by the selector,outputs from the INF 15 after necessary processing. On the other hand,the signal not selected by the selector is discarded. Accordingly, theside of the signal selected by the selector is set in an active state.Switching control of the selector of the INF 15 is carried out by theswitching control section.

Hereinafter, the components of the main device 110, and the expansiondevices 210, 310 will individually be described.

(MUX/DMUX Sections)

The MUX/DMUX sections 120 and 130 of the main device 110 serve as signalmultiplexing/demultiplexing functions of the communication units 16 aand 16 b shown in FIG. 5 (multiplexers/demultiplexers). The MUX/DMUXsection (WK) 120 belongs to the WK side, and the MUX/DMUX section (PT)130 belongs to the PT section.

The MUX/DMUX sections 120 and 130 carry out similar operations. Toexplain by taking the example of the MUX/DMUX section 120, a signalwhich is a result of conversion of an optical signal received by eachINF 15 of the main device 110 from the other device into an electricsignal, and signals which are results of conversion of optical signalsreceived by the receiving sections 122 and 124 from the expansiondevices 210 and 310 into electric signals are input to the MUX/DMUXsection 120. The MUX/DMUX section 120 multiplexes or demultiplexes theinput signal when necessary, and inputs to the signal connectionconverting section 121.

The signal connection converting section 121 switches an outputdestination of each input signal according to its address. The MUX/DMUXsection 120 multiplexes or demultiplexes each signal output from thesignal connection converting section 121 when necessary, and sends toone of the INF 15 and the transmitting sections 123 and 125 according toits address.

The MUX/DMUX sections 220 and 230 (320 and 330) of the expansion devices210 and 310 are different from the MUX/DMUX sections 120 and 130 in thatno signal connection converting section is disposed to unify signalconnection management. The MUX/DMUX sections 220 and 230 (320 and 330)include receiving and transmitting sections. The MUX/DMUX section 220(320) is connected through the optical fiber 410 a (410 c) to theMUX/DMUX section 120. The MUX/DMUX section 230 (330) is connectedthrough the optical fiber 410 b (410 d) to the MUX/DMUX section 130.

(Transmitting Section and Receiving Section)

Receiving sections 122 and 124 of the MUX/DMUX section 120 of the WKside have functions of receiving optical signals of the WK sidetransmitted from the expansion devices 210 and 310 (MUX/DMUX sections220 and 320) through the optical fibers 410 a and 410 c, converting intoelectric signals, and outputting. The transmitting sections 123 and 125of the MUX/DMUX section 120 convert signals to be sent to the WK sides(MUX/DMUX sections 220 and 320) of the expansion devices 210 and 310into optical forms, and send to the optical fibers 410 a and 410 c.

Receiving sections 132 and 134 of the MUX/DMUX section 130 of the PTside have functions of receiving optical signals of the PT sidetransmitted from the expansion devices 210 and 310 (MUX/DMUX sections230 and 330) through the optical fibers 410 b and 410 d, converting intoelectric signals, and outputting. The transmitting sections 133 and 135of the MUX/DMUX section 130 convert signals to be sent to the PT sides(MUX/DMUX sections 230 and 330) of the expansion devices 210 and 310into optical signals, and send to the optical fibers 410 b and 410 d.Various trouble information, and information for unit switching are alsotransmitted/received.

(Signal Connection Converting Section)

The signal switching converting sections 121 and 131 are realized by thecrossconnecting functions of the communication units 16 a and 16 b, andpresent in the MUX/DMUX sections 120 and 130 of the main device 110. Thesignal connection converting section executes signal connectionswitching between the INF units 15 of the main device 110 and theexpansion devices 210 and 310. Accordingly, as compared with managementof the signal connection switching executed by each optical transmissiondevice, it is possible to simplify management based on unifiedmanagement by one optical transmission device of the describedconstitution.

(State Monitoring Section)

The state monitoring section 17 a is a function realized by the CPU unit17. The state monitoring section 17 a monitors states of thecommunication units 16 a and 16 b, a trouble state of the optical line,and a state of an APS (Auto Protection Switch). Note that, a manual unitswitching operation is enabled. The APS state means a unit switchingstate, i.e., a current switching state or the like in which an operationis carried out in the working unit or the protection unit.

The state monitoring section 17 a communicates with state monitoringsections 27 a and 37 a of the expansion devices 210 and 310, andtransmits information regarding a state managed by itself or the like tostate monitoring sections 27 a and 37 a through the communication paths41 a and 41 c.

(Switching Managing Section)

The switching managing section 17 b of the main device 110, and theswitching managing sections 27 b and 37 b of the expansion devices 210and 310 are functions realized by the CPU units 17, 27, and 37. Theswitching managing section 17 b corresponds to the main device sidetrouble information collecting section, the receiving section, theintegrating section, the storing section, the converting section, thetotaling section, the deciding section, and the main device side WK/PTswitching control section of the present invention. The switchingmanaging sections 27 b and 37 b correspond to the expansion device sidetrouble information collecting sections, the transmitting sections, andthe expansion device side WK/PT switching control sections of thepresent invention.

Each switching managing section manages unit switching between the WKand PT units of its own shelf. According to this embodiment,determination processing of unit switching is managed in a unifiedmanner by the switching managing section 17 b of the main device 110.Thus, the switching managing section 17 b of the main device 110 isdifferent in function from the switching managing sections 27 b and 37 bof the expansion devices 210 and 310.

First, the function of the switching managing section 27 b (37 b) of theexpansion device side will be described. The switching managing section27 b of the expansion device side manages unit switching between the WKand PT sides. The switching managing section 27 b mainly has thefollowing functions.

The switching managing section 27 b realizes a trouble informationcollecting function of collecting unit trouble information of its ownoptical transmission device, line trouble information, and the like.That is, as described above with reference to FIG. 2, the switchingmanaging section 27 b collects trouble information regarding line andunit troubles of the communication units 26 a and 26 b of the WK and PTsides.

Here, the unit trouble information means information regarding a unitfailure such as a failure of a unit substrate, a unit trouble such asreleasing of a unit from the state of being mounted to the opticaltransmission device, a power supply trouble or the like. The linetrouble information means information regarding an optical signaltrouble such as a signal loss (LOS) or a frame loss (LOF).

The switching managing section 27 b executes first-stage integration ofthe collected trouble information. That is, for each of the WK and PTsides, the switching managing section 27 b creates first integratedinformation equivalent to the first integrated information 24 adescribed above with reference to FIG. 2 which integrates the collectedtrouble information for each communication unit.

The first-stage integration means conversion of the collected troubleinformation into information which integrates contents thereof. In thiscase, for example, information indicating line troubles are integrated(converted) into information regarding SD-1, SD-2, . . . SD-n (SD:Signal Degrade: signal degradation, the number after “−” indicates thenumber of trouble lines), SF-1, SF-2, . . . SF-n (SF: Signal Fail:signal failure, the number after “−” indicates the number of troublelines), and NR (No request: no alarm) or the like. The unit trouble isrepresented by SF-n (n: maximum number of lines). Then, the switchingmanaging section 27 b notifies the first integrated information of theWK and PT sides to the switching managing section 17 b of the maindevice 110. The switching managing section 37 b executes processingsimilar to that of the switching managing section 27 b.

Next, the function of the switching managing section 17 b of the maindevice side will be described. The switching managing function 17 bmainly has the following functions. First, as in the case of theswitching managing section 27 b of the expansion device side, theswitching managing section 17 b collects unit trouble information of itsown shelf, line trouble information, and the like, and creates firstintegrated information of the WK and PT sides (equivalent to the firstintegrated information 14 a to 14 d described above with reference toFIG. 2) for each expansion device.

Second, the switching managing section 17 b creates second integratedinformation. That is, the switching managing section 17 b receives thefirst integrated information notified from each of the expansion devices210 and 310, and creates second integrated information which integratescorresponding first integrated information (equivalent to the secondintegrated information 49 a to 49 d described above with reference toFIG. 3) for each of the WK and PT sides, and each of the expansiondevices 210 and 310 by using the first integrated information created byitself and the notified first integrated information.

According to this embodiment, one of triggers to collect the firstintegrated information is a hardware interruption when each troubleoccurs. Thus, a case may be imagined in which by a certain timing a newtrouble occurs in the expansion device 210 alone while no new troublesoccur in the other optical transmission devices. In this case, firstintegrated information is not created in all the optical transmissiondevices each time. The main device 110 uses the previous firstintegrated information regarding the optical transmission device inwhich no new troubles occur when the main device 110 creates secondintegrated information.

For example, it is assumed that a new trouble occurs in the expansiondevice 210 alone. In such a case, first, the switching managing section17 b receives the first integrated information notified from theexpansion device 210 (in this case, no first integrated information isnotified from the expansion device 310). Then, the switching managingsection 17 b creates second integrated information by using the firstintegrated information created by itself previously, new firstintegrated information notified from the expansion device 210, and thefirst integrated information previously notified from the expansiondevice 310. Accordingly, it is possible to create integrated informationof the entire system more quickly when a trouble occurs.

Third, the switching managing section 17 b converts each secondintegrated information into a trouble point. Fourth, the switchingmanaging section 17 b compares trouble points of the WK ands PT sideswith each other, and executes unit switching determination. Fifth, theswitching managing section 17 b notifies unit switching informationdecided by the unit switching determination to the expansion devices 210and 310.

The main device 110 and the expansion devices 210 and 310 areinterconnected through the optical fibers 410 a to 410 d. Thecommunication paths 41 b and 41 d are disposed to execute mutualinformation transfer between the switching managing section 17 b of themain device 110 and the switching managing sections 27 b and 37 b of theexpansion devices 210 and 310. The switching managing sections 27 b and37 b transmit the collected trouble information (first integratedinformation) of their own optical transmission devices (expansiondevices 210 and 310) through the communication paths 41 b and 41 d tothe switching managing section 17 b. The switching managing section 17 btransmits the unit switching information decided by the unit switchingdetermination through the communication paths 41 b and 41 d to theswitching managing sections 27 b and 37 b.

Each of the communication paths 41 b and 41 d is disposed on each of theoptical fibers 410 b and 410 d of the PT side. Note that, the statemonitoring section 17 a transfers information with the state monitoringsections 27 a and 37 a through the communication paths 41 a and 41 c.The communication paths 41 a and 41 c are constituted by using properlines on the optical fibers 410 a to 410 d.

<<Message Exchanged Between Switching Managing Sections>>

Next, description will be made of messages exchanged between theswitching managing section 17 b of the main device and the switchingmanaging sections 27 b and 37 b of the expansion devices 210 and 310.FIG. 7A is an explanatory diagram of a message transmitted from the maindevice 110 to each of the expansion devices 210 and 310. FIG. 7B is anexplanatory diagram of a message transmitted from each of the expansiondevices 210 and 310 to the main device 110.

Information is exchanged by using an overhead byte set on a SOH (sectionoverhead) of a frame format defined by SONET (Synchronous OpticalNETwork) which is a high-speed digital communication system using anoptical fiber. In this case, a K1/K2 byte used for executing normal lineswitching in the SOH is used. A method of using the K1/K2 bytes isdefined according to a standard. However, according to this embodiment,since being used for unit switching, a standard overhead using method ischanged.

As shown in FIG. 7A, the K1 byte transmitted from the main device to theexpansion device is divided into upper 4 bits and lower 4 bits. In theupper 4 bits, a trouble code indicating a cause of system switching isset as a trouble code (trouble information). In the lower 4 bits, aswitching state, i.e., switching instruction for the expansion device,is set. Here, one of switching instruction for the PT side “0:PT” andswitching instruction for the WK side “1:WK” is set.

In addition, as in the case of the K1 byte, the K2 byte transmitted fromthe main device to the expansion device is divided into upper 4 bits andlower 4 bits. In the upper 4 bits, a trouble code indicating contents oftrouble information (first integrated information) of the PT side (PT)of the own optical transmission device (main device 110) is set astrouble code (trouble information). The lower 4 bits are not used as areservation area.

On the other hand, as shown in FIG. 7B, the K1 byte transmitted fromeach expansion device to the main device is divided into upper 4 bitsand lower 4 bits. In the upper 4 bits, a trouble code indicatingcontents of trouble information (first integrated information) of the WKside (WK) of the own shelf (each of the expansion devices 210 and 310)is set as trouble information. In the lower 4 bits, a code indicating acurrent switching state of the own shelf is set as a switching state.

The K2 byte transmitted from the expansion device to the main device isalso divided into upper 4 bits and lower 4 bits. In the upper 4 bits, atrouble code indicating contents of trouble information (firstintegrated information) of the PT side (PT) of the own shelf (each ofthe expansion devices 210 and 310) is set as trouble information. Thelower 4 bits are not used as a reservation area.

Now, the trouble codes set in the K1 byte and the K2 byte will bedescribed. In the example, the trouble codes take values of “0” to “14”.“NR (No Request)” is allocated to the trouble code “0”. The “NR”indicates that there are no troubles to be notified. “MAN (MANualswitching request)” is set for the trouble code “7”.

“SD (Signal Degrade: signal degradation)-x” is allocated to each of thetrouble codes “8” to “10”. “SF (Signal Fail: signal failure)-x” isallocated to each of the trouble codes “11” to “13”. The “x” is a valueindicating a degree of signal degradation. According to the embodiment,each of the optical fibers 410 a to 410 d for connecting thecommunication units is composed of three optical tape fibers. The numberof optical tape fibers having lines of troubles (signal degradation orsignal failure) is set to a value of the “x”. Thus, one of values of “1”to “3” is set for the “x” according to the number of optical tape fibersof troubles. As a value of the “x” is larger, a degree of a trouble ishigher. Further, “FRCD (FORCED: forced switching) is allocated to thetrouble code “14”. The “FRCD” means switching more forcible than the“MAN” of the trouble code “7”.

In each of FIGS. 7A and 7B, one trouble code indicating contents of thefirst integrated information is notified. Thus, each of the switchingmanaging sections 17 b, 27 b, and 37 b is constituted to create firstintegrated information according to trouble priority definition (degreeof a trouble) similar to that shown in FIG. 5, and notify acorresponding trouble code.

For example, it is assumed that the switching managing section 27 bdetects “(3)-F” and “(3)-D” for the three optical tape fibersconstituting the optical fiber 410 a as trouble information for the WKside. It is also assumed that there are one signal degradation and onesignal failure for each of the three optical fibers. In this case,“SD-1” and “SF-1” are obtained as trouble information. Accordingly, if aplurality of kinds of trouble information are obtained, the switchingmanaging section 27 b selects trouble information of a highest troubledegree as first integrated information according to the troublepriority. In the example, since the “SF-1” is higher in trouble prioritythan the “SD-1”, the “SF-1” is selected as first integrated information,and becomes a target of notification.

The number of troubles for the SD or the SF is notified as describedabove, whereby a switching state in which signal cutting-off due to atrouble is more difficult to occur can be determined. However, accordingto the embodiment, as described above, the notification of the switchingstate is executed between the switching managing sections through thecommunication paths (41 b and 41 d) using any one of optional opticaltape fiber of the protection side. Thus, if a trouble occurs in theoptical tape fiber in which the communication paths 41 b and 41 d areformed, a value of the “x” is set to a maximum (3). This means that thetrouble is treated as a largest trouble because impossible reception ofthe state notification creates a possibility of a contradiction inswitching in the entire system.

The overhead using method shown in FIG. 7 can increase a use rate ofline switching software by making a format similar to that definedaccording to the standard of GR253.

<<Trouble Point>>

Next, description will be made of the function of the switching managingsection 17 b to convert the second integrated information into a troublepoint. As described above, the switching managing section 17 b createsthe second integrated information that integrates the first integratedinformation. The second integrated information is created by a methodsimilar to that of the first integrated information. That is, asinformation to create the second integrated information, firstintegrated information of the main device side and first integratedinformation of the expansion device side are prepared. The switchingmanaging section 17 b determines large and small trouble priority of thefirst integrated information, and selects the higher first integratedinformation as the second integrated information.

For example, when the second integrated information of the WK side iscreated between the main device 110 and the expansion device 210, theswitching managing section 17 b compares the trouble priority of thefirst integrated information of the WK side of the main device 110 sidewith that of the first integrated information of the WK side of theexpansion device 210. At this time, if the first integrated informationof the main device side is “SF-1” and that of the expansion device sideis “SD-1”, the switching managing section 17 b selects the “SF-1” as thesecond integrated information.

Here, the trouble priority is set to be higher as the number of opticaltape fibers having troubles is higher in the case of troubles of thesame kind. Thus, for example, if the first integrated information of themain device side is “SD-3”, and that of the expansion device side is“SD-1”, the switching managing section 17 b selects the “SD-3” as thesecond integrated information.

In the case of a mixture of SD and SF troubles, the “SF-1” is set to behigher in trouble priority than the “SD-3”. This is because signalcutting-off occurs in the case of the SF while signal deterioration isrecognized but no signal cutting-off occurs in the case of the SD.

When the switching managing section 17 b converts the second integratedinformation into a trouble point, the switching managing section 17 brefers to a trouble point conversion table as shown in FIG. 8. Forexample, the trouble point conversion table is created in the memory ofthe CPU unit 17. The switching managing section 17 b executes conversioninto a trouble point by reading the trouble point corresponding to thesecond integrated information from the trouble point conversion table.

In the trouble point conversion table, each trouble point is previouslydefined to match the trouble priority shown in FIG. 5. The troublepriority is a value indicating seriousness of a trouble, and a higherpriority means a more serious trouble situation. Thus, a trouble pointvalue is set to be higher as priority is higher.

For example, in the case of occurring an SD or SF trouble, a higherpoint is defined as the number of trouble lines in the trouble type islarger. That is, a trouble point of an “SD(SF)-2” is set to be higherthan a trouble point of an “SD(SF)-1”. Note that, trouble points are notuniformly distributed, but points are set according to seriousness oftroubles.

Further, in the example shown in FIG. 8, for “SF-3”, values of troublepoints are different between the WK side (working side) and the PT side(protection side). According to this embodiment, a switching state isnotified by using any one of optional optical tape fiber of theprotection side. Thus, when SF occurs in the optical tape fiber,switching notification cannot be executed. Upon detection of the SF ofthe optical tape fiber, the expansion device forcibly executes unitswitching to the working side. In this case, the trouble point of the“SF-3” of the protection side is set to be higher than the trouble pointof the “SF-3” of the working side so that the main device can follow theswitching operation of the expansion device. Thus, when the troubleinformation of the working side and the trouble information of theprotection side in the entire system are integrated to be “SF-3”, atrouble point of the protection side is set to be larger.

A unit trouble is treated as independent trouble information in the maindevice, and a trouble point is defined to be higher than that of a linetrouble (SD or SF). A unit trouble of the main device side is definedsuch that a trouble point of the protection side is higher than that ofthe working side. Note that, a unit trouble of the expansion device istreated as an SF trouble, and defined by SF-3.

Upon creation of the second integrated information for each expansiondevice, the switching managing section 17 b converts each secondintegrated information into a trouble point. Subsequently, the switchingmanaging section 17 b totals trouble points for the working side and theprotection side. Then, the switching managing section 17 b compares atotaling result of the working side with a totaling result of theprotection side to determine which is larger.

Then, the switching managing section 17 b decides the side of thesmaller totaling result as a switching state to be selected by theoptical transmission system. That is, if the trouble point of theworking side is smaller than that of the protection side, the workingside is decided as a switching state to be selected. If the troublepoint of the protection side is smaller than that of the working side,the protection side is decided as a switching state to be selected.

Subsequently, when the decided switching state does not coincide with acurrent switching state, the switching managing section 17 b executesunit switching of its own optical transmission device (main device 110),and notifies the expansion devices 210, 310 of a switching instruction.Determination conditions may be added such that switching is executedonly when a larger value of a trouble point exceeds a predeterminedvalue in the switching determination (determination by comparison of thecollecting results with each other). In addition, items (troubles)corresponding to trouble points can be added or point values can bechanged in the trouble point conversion table shown in FIG. 8 so that anintended determination result of large and small comparison can beobtained.

OPERATION EXAMPLE

Next, referring to FIGS. 9, 10, and 11, operations of the switchingmanaging sections 17 b and 27 b will be described. FIG. 9 is a diagramshowing a functional block of the switching managing section. FIG. 10 isa flowchart showing an operation example of the switching managingsection 27 b of the expansion device. FIG. 11 is a flowchart showing anoperation example of the switching managing section 17 b of the maindevice.

To explain the operations of the switching managing sections, first,referring to FIG. 9, a functional constitution of the switching managingsection will be described. In FIG. 9, the switching managing section 17b (27 b) functions as a device which includes an interruption processingsection 171, a switching trigger collecting section 172, a constitutioninformation management processing section 173, a state monitoringinterface function section 174, a unit switching processing section 175,a WK/PT switching processing section 176, a BLSR switching processingsection 177, and a path switching processing section 178. Here, thefunctions for unit switching will mainly be described.

(Interruption Processing Section)

The interruption processing section 171 processes interruptionsoccurring when various trouble changes occur or when unit switching isnotified, and notifies the switching trigger collecting section 172. Theinterruptions processed by the interruption processing section 171include a unit trouble change, a line trouble change, and an APS change.

The unit trouble change is an interruption occurring when a troubleconcerning a unit (each of STS-SF 16 a and 16 b) occurs. For example,there are a FLT (unit failure such as unit substrate damage), RMVD(removal of a unit from the optical transmission device), a PWR FAIL(power supply trouble), and the like.

The line trouble change is an interruption occurring when a troubleconcerning the optical line occurs. There are a LOS (Loss of Signal:signal input cut-off), a LOF (Loss of Frame: asynchronization of frame),an AIS (Alarm Indication Signal: trouble notifying signal from anoptical repeater or the like), a BERSF (Signal Failure: serioustrouble), BERSD (Signal Degradation: light trouble), and the like.

The APS change is an interruption occurring when a unit switchingnotification from the switching managing section 17 b of the main deviceto the expansion device, trouble information integrated by the switchingmanaging section 27 b of the expansion device, unit switchinginformation of the expansion device, or the like comes in.

(Switching Trigger Collecting Section)

The switching trigger collecting section 172 includes a unit switchingsection 179, a WK/PT switching section 180, and a BLSR switching section181.

The switching trigger collecting section 172 collects troubleinformation which cause the interruptions based on the interruptioninformation notified by the interruption processing section 171,determines necessary processing based on the collected various troubleinformation, and notifies each processing section. Then, the collectedtrouble information in the trouble information such as the SD-x or SF-xdescribed above are integrated, and notified to the unit switchingsection 179.

The unit switching section 179 integrates the trouble informationnotified by the switching trigger collecting section 172 for the workingside and the protection side, and creates APS information. Then, the APSinformation is notified to the unit switching processing section 175.

The APS information is a unit switching notification sent from theswitching managing section 17 b of the main device to the expansiondevice side, trouble information integrated by the switching managingsection 27 b of the expansion device, unit switching information of theexpansion device, or the like.

(Unit Switching Processing Section)

The unit switching processing section 175 transmits the APS informationnotified by the unit switching section 179 to the other opticaltransmission device by the transmitting section (e.g., 123 in FIG. 1) ofthe MUX/DMUX section of each unit. In addition, based on the APSinformation, unit switching is executed when unit switching of its ownoptical transmission device is necessary.

(State Monitoring Interface Function Section, Constitution InformationManagement Processing Section)

The state monitoring interface function section 174 is an interfacebetween the state monitoring section 17 a and the switching managingsection 17 b, and issues a manual unit switching instruction or the likefrom the state monitoring section 17 a to the constitution informationmanagement processing section 173.

The constitution information management processing section 173 obtainsinformation regarding a unit switching state, a line state or the likemonitored by the state monitoring section 17 a from the switchingtrigger collection section 172, and issues the unit switchinginstruction from the state monitoring section 17 a to the switchingtrigger collecting section 172.

(Other Constitutions)

Other constitutions not directly concerning unit switching will brieflybe described. The WK/PT switching section 180 determines switching ofthe lines of the WK side/PT side prepared for each optical line, andnotifies the WK/PT switching processing section 176. Accordingly, theWK/PT switching processing section 176 executes line switching of the WKand PT sides for each optical line (not unit). The BLSR switchingsection 181 determines bypass line switching at the time of a linetrouble by a BLSR (Bidirectional Line Switched Ring) system, andnotifies the BLSR switching processing section 177. Thus, the BLSRswitching processing section 177 executes line bypassing by the BLSRsystem. The path switching processing section 178 executes signalswitching at a path level between terminals.

(Explanation of Operation Flow)

Next, referring to FIG. 10, an operation of the switching managingsection 27 b of the expansion device will be described. Wheninterruptions such as various trouble changes occur, the interruptionprocessing section 171 of the switching managing section 27 b processesthe interruptions, and notifies the switching trigger collecting section172 (see FIG. 9).

Next, in the switching trigger collecting section 172, interruptioncause summary information are collected to determine causes of theinterruptions (S01). Then, determination is made as to whether theinterruption causes are troubles concerning a unit or not based on theinterruption cause summary information (S02). If those are troublesconcerning the unit (S02; YES), unit trouble information are collected(S05), and notified to the unit switching section 179.

If those are not troubles concerning the unit (S02;NO), determination ismade as to whether the interruption causes are troubles concerning theoptical line or not (S03). If those are troubles concerning the line(S03; YES), trouble information for the line are collected (S06), andnotified to the unit switching section 179. If those are not troublesconcerning the line (S03; NO), determination is made as to whether theinterruption causes are APS changes or not (S04). If the interruptioncauses concern the APS changes (S04; YES), APS information are collected(S08), and notified to the unit switching section 179.

Upon reception of the notification from the switching trigger collectingsection 172, the unit switching section 179 executes processingaccording to each notification. If an occurrence cause is a unit troubleor a line trouble, the collected unit and line trouble information areintegrated for each unit of the working side or protection side (S07),and APS information (equivalent to first integrated information) such asSD-x, SF-x or NR is created (S11).

If an occurrence cause is an APS change, the notified APS information isa switching notification from the main device 110. In this case, theunit switching section 179 determines whether or not to executeswitching processing based on the switching notification (S09), andpasses a result of the determination to the unit switching processingsection 175. The unit switching processing section 175 executes unitswitching according to the determining result of the switchingnotification (S10). The unit switching section 179 creates a unit stateafter the switching as APS information (S11). After the creation of theAPS information, the APS information is notified to the unit switchingprocessing section 175.

The unit switching processing section 175 transmits the APS informationto the main device 110 through a message using the overhead portion (seeFIG. 7) by the communication unit of the protection side (S12).

Lastly, the switching trigger collection section 172 newly checkswhether or not a trouble change has occurred by occurrence of a newinterruption, and ends in case where no change has occurred (S13 and14). If no change has occurred, the process ends. If a change hasoccurred, the process returns to the determining processing (S02) againto execute the processing. Note that, the switching managing section 37b of the expansion device 310 executes similar processing.

Next, referring to FIG. 11, an operation of the switching managingsection 17 b of the main device will be described. In FIG. 11,operations of steps S01 to 08 and S12 to 14 are similar to those of theswitching managing section 27 b of the expansion device, and thus theyare denoted by similar reference numerals to reference numerals of FIG.10. Operations different from those of the switching managing section 27b of the expansion device alone will be described.

As described above, the APS information of the expansion device istransmitted to the main device 110 from each of the switching managingsections 27 b, 37 b of the expansion devices. The APS information fromthe expansion device is determined to be an APS change (S04). Then, suchAPS information are collected (SO8), and notified to the unit switchingsection 179.

Upon reception of the notification from the switching trigger collectionsection 172, the unit switching section 179 integrates troubleinformation of the main device and the expansion device for each of theworking/protection (S21). In other words, trouble types shown in FIG. 8are created for each of the working/protection of each opticaltransmission device. The integrating processing (S21) of the troubleinformation will be described more in detail. If it is determined to bean APS change in S04, i.e., if a new trouble occurs in the expansiondevice, APS information collected in S08 are trouble informationregarding the expansion device undergoing the new trouble occurrence. Inthis case, to integrate the trouble information (S21), the unitswitching section 179 uses the previous trouble information as troubleinformation of the main device and the expansion device in which no newtroubles occur. In addition, if it is determined to be a UNIT trouble ofthe own shelf (main device) in S02, it is trouble information of the ownoptical transmission device that are collected in S05. In this case, tointegrate the trouble information (S21), the unit switching section 179uses the previous information as trouble information for each expansiondevice.

Next, based on each integrated information, the unit switching section179 refers to the table of FIG. 8 to execute conversion into a troublepoint for each of the working and protection sides (S22). Then, thetrouble points are compared with each other (S23), unit switchingdetermination is made based on a result of the point comparison, andunit switching is executed by the unit switching processing section 175(S24). In this case, the point comparison may be large and smallcomparison.

Then, APS information is creased as a unit switching notification to theexpansion device (S25), and the unit switching processing section 175 isrequested to transmit the APS information (S12).

Operation Effects of Embodiment

According to the optical transmission system of this embodiment, the twocommunication units of the working side (WK) and the protection side(PT) are prepared for each of the optical transmission devices whichconstitute the system, and the optical transmission devices aresynchronized with each other to execute unit switching so that one ofthe WK and PT sides can be selected in the entire system.

To determine such unit switching, the switching managing sections 27 band 37 b of the expansion devices 210 and 310 create first integratedinformation which integrates trouble information regarding the opticalfibers 410 a and 410 b for connecting the communication units of the WKand PT sides, and notifies the switching managing section 17 b of themain device 110.

The switching managing section 17 b creates first integrated informationfor each of the WK and PT sides and each expansion device, and createssecond integrated information, which integrates the first integratedinformation notified by each of the expansion devices 210 and 310 andthe first integrated information which has been created by itself, foreach of the WK and PT sides and each expansion device.

Subsequently, the switching managing section 17 b converts each of thesecond integrated information into a trouble point. A smaller value ofthe trouble point indicates a better trouble state. Trouble points aretotaled for each of the WK and PT sides. Then, the switching managingsection 17 b compares large and small results of the totaling, andselects a smaller trouble point. Accordingly, the side of a bettertrouble state is specified. At this time, if the side selected as aresult of determination is different from a currently selected side,unit switching is executed.

As described above, according to this embodiment, instead of determiningwhich of a plurality of trouble patterns a current trouble situationbelongs to by preparing the plurality of trouble patterns beforehand toexecute unit switching, unit switching is determined by converting thecurrent trouble situation into points, and comparing the points betweenthe WK and PT sides. Thus, since determining processing necessary forthe unit switching is greatly reduced, it is possible to shorten a timenecessary for switching determination, and to shorten a time necessaryfor the unit switching.

That is, to execute unit switching determination, the unit switchingsection 179 of the main device 110 integrates trouble information ofeach unit and converts into a numerical value of a trouble point.Accordingly, subsequent switching determination only requires large andsmall comparison of trouble points between the working side and theprotection side, and thus the switching determination can be completedwithin a short time.

The main device notifies a result of the switching determination throughthe optical line to each expansion device, and the expansion deviceexecutes switching according to switching instruction issued from themain device. By employing such a constitution, the expansion device neednot execute switching determination, and a total switching time of thesystem (configured by combining the plurality of optical transmissiondevices) can be shortened.

Since the switching determination needs the trouble point comparisonalone, a test of switching determination only becomes point comparisonprocessing in quality evaluation, and an evaluation time can be greatlyshortened. Further, a test pattern in quality evaluation only needs toguarantee a normal operation of conversion processing into a troublepoint. Thus, enumeration of test patterns is improved, and higherquality functions can be guaranteed.

In addition, since each trouble information is lastly converted into anumerical value, judgment can be made by the same determination such ascomparison of numerical values under any trouble situations. In theswitching determination, determination conditions that a threshold valueis preset and switching is executed when the trouble point exceeds thethreshold value, may be added, and future functional expansion will befacilitated.

Furthermore, the trouble point conversion table shown in FIG. 8 enablesaddition of trouble types and arbitrary change of the switchingdetermination by changing the point value itself. Besides, such a changeonly needs change of table contents, and thus the change or the like canbe facilitated.

<<Case of Communication Cut-off between Main Device and ExpansionDevice>>

As describe above, the APS information such as the unit switchingnotification is notified through one optical tape fiber for connectingthe communication units of the protection and by using the K1/K2 byte ofthe overhead portion shown in FIG. 7. Then, the expansion devices 210and 310 execute switching according to the switching notification fromthe main device 110, whereby unit switching between the working and theprotection of each optical transmission device is synchronized in thesystem.

Now, referring to FIG. 12, description will be made of a unit switchingoperation of the expansion device when communication with the maindevice is cut off. FIG. 12 is a flowchart of an operation of theswitching managing section 27 b of the expansion device when thecommunication with the main device is cut off, expanding processingafter S06 more in detail in the operation flow of the switching managingsection 27 b at a normal time shown in FIG. 10. Accordingly, theprocessing after S06, i.e., S31, S32, will be described. Otherprocessing is similar to that of the normal time.

When an interruption occurs, and a cause of the interruption concerns aline trouble, the switching trigger collecting section 172 collects linetrouble information (S06, similar to that of the normal time).

Subsequently, from the collected line trouble information, determinationis made as to an abnormality in a line for transmitting/receiving APSinformation with the main device, and disconnection (S31). If the lineis not cut off, processing after S07 is executed as similar as in thecase of normal processing. However, if the line has been cut off, aprocessing is executed to forcibly switch an active unit of the ownoptical transmission device (expansion device) to the working side(S32). Then, APS information indicating a unit state after switching iscreated, and processing similar to that of the normal time is executedthereafter (S11 and the subsequent steps). On the main device side,determination is made in S04 upon reception of the APS information, andprocessing similar to the normal processing is executed thereafter. As aresult, unit switching to the working side occurs in the main device.

If a trouble occurs in the line for transmitting/receiving the APSinformation, i.e., if the communication of the expansion device with themain device is cut off, the system is put in a situation in which unitswitching cannot be synchronized, leading to a problem such as signalcutting-off at the end. Thus, under such a situation, a constitution isemployed in which the expansion device always switches the unit to theworking side.

Thus, even when the expansion device cannot receive the switchingnotification from the main device, unified unit switching is enabled inthe entire shelf, and redundancy can be realized for the system.

<<Case of Removal of Expansion Device from Main Device>>

A situation is conceivable in which the line between the main device andthe expansion device is set in a signal cut-off state for both of theworking and protection sides. In other words, a situation may occur inwhich the main device 110 cannot receive a transmission signal from acertain expansion device at all. In such a case, a constitution isemployed in which the main device 110 of this embodiment excludes theexpansion device of the signal cut-off state from switchingdetermination of the entire system.

Now, referring to FIG. 13, in the above case, unit switchingdetermination of the main device 110 will be described. FIG. 13 is aflowchart of an operation of the switching managing section 17 b of themain device when the expansion device is excluded from unit switchingdetermination, expanding processing of S12 more in detail in theoperation flow of the switching managing section 17 b at the normal timeshown in FIG. 11. Thus, S21 alone will be described. Other processing issimilar to that of the normal time.

Upon reception of the unit and line trouble information integrated foreach unit of the working and protection sides (S07) by the switchingtrigger collecting unit 172, the switching managing section 17 bintegrates trouble information of the main device and the expansiondevice for each of the working and protection (S21). In this event,based on the trouble information collected as the line troubles of theown optical transmission device (main device), i.e., information thatthe own optical transmission device as a receiving side determines aline trouble between the expansion devices (e.g., 14 a shown in FIG. 3),determination is made as to whether or not there is a expansion devicein which SF troubles (SF-x: x=maximum number of lines) occur on both ofworking and protection sides (S211). In the case that it determines nodevice, the expansion device is counted out from switchingdetermination, and trouble information not including that of theexpansion device are integrated for each of the working and protectionsides (S212). As a result of the determination, such a expansion deviceis not included, all information are integrated for each of the workingand protection as in the normal case (S213). Then, trouble pointconversion is executed based on the integrated information (S22), andprocessing similar to the normal processing is executed thereafter.

A constitution is employed in which when signal cut-off states are seton both of the working and protection sides for the main device in theline with the expansion device, the main device of this embodimentcounts out the expansion device of the signal cut-off state fromswitching determination of the entire system.

Thus, by executing unit switching determination with priority given to arelation with a normal expansion device, unit switching of higherredundancy is realized.

MODIFIED EXAMPLE

According to the embodiment of the present invention, the number ofexpansion devices is two. However, even when the number is three ormore, the above switching determination based on the trouble points canbe directly used, and for example, a state can be decided by large andsmall comparison.

In addition, since the number of expansion devices as a target oftrouble collection only increases, the current processing can be usedfor addition of trouble points, and the added number only increases, andfunctional expansion can be facilitated.

Furthermore, there is a case in which the expansion device and the maindevice are interconnected through more optical fibers. Such the case canbe dealt with by slightly changing the way to use K1/K2 bytes shown inFIG. 7. In this case, in the information notified by the expansiondevice (FIG. 7B), an area of “SWITCHED STATE” of the K1 byte is set forthe number of trouble lines, and an area of “TROUBLE INFORMATION” is setfor a trouble type only (SD/SF), whereby 256 kinds can be dealt with atmaximum. The K2 byte can be similarly dealt with by setting an area of“RESERVED” for the number of trouble lines. In this case, a switchedstate of the expansion device cannot be determined by the main device.However, since there is rule established that the expansion device sidealways complies with a switching notification state from the maindevice, and the expansion device cannot receive the switchingnotification from the main device side unless it complies, the switchedstate of the expansion device can be guessed by the main device evenwithout the switched state notification from the expansion device. As aresult, no problems occur even without the switched state notificationfrom the expansion device.

1. An optical transmission system including a plurality of opticaltransmission devices, comprising: a main device; and a plurality ofexpansion devices, the plurality of optical transmission devices areconfigured by the main device and the plurality of expansion devices,wherein the main device and the plurality of expansion devices includesa plurality of interface units controlling signaltransmission/reception, and each multiplexing/demultiplexing section ofeach of working and protection sides multiplexing/demultiplexing asignal transmitted/received by each interface unit, themultiplexing/demultiplexing section of the working side of eachexpansion device is connected through a plurality of optical lines tothe multiplexing/demultiplexing section of the working side of the maindevice, the multiplexing/demultiplexing section of the protection sideof each expansion device is connected through a plurality of opticallines to the multiplexing/demultiplexing section of the protection sideof the main device, the multiplexing/demultiplexing section of each ofthe working and protection sides of the main device includes a switchingsection switching an output destination of a signal input to each of themain device and the plurality of expansion devices according to anaddress of the signal, each of the plurality of expansion devicesincludes: a expansion device side trouble information collecting sectioncollecting trouble information, indicating a trouble state of one ormore optical lines among the plurality of optical lines for receiving asignal from the main device, for each of the working and protectionsides; a transmitting section transmitting the collected troubleinformation of the working and protection sides to the main device; anda expansion device side working/protection switching control sectioncontrolling switching between the working and protection sides accordingto a switching instruction between the working and protection sidesreceived from the main device, and the main device includes: a maindevice side trouble information collecting section collecting troubleinformation indicating a trouble state of, among the plurality ofoptical lines for connecting between the main device and the expansiondevices, one or more optical lines for receiving a signal from each ofthe expansion devices for each of the working and protection sides andeach expansion device; a receiving section receiving the troubleinformation of the working and protection sides collected by theexpansion device side trouble information collecting section from theexpansion device; an integrating section creating integrated troubleinformation integrating the trouble information collected by the maindevice side trouble information collecting section and the troubleinformation collected by the expansion device side trouble informationcollecting section for each of the working and protection sides and eachexpansion device; a storing section storing point informationcorresponding to the integrated trouble information; a convertingsection converting the integrated trouble information into the pointinformation stored in the storing section; a totaling section totalingthe converted point information regarding each of the working andprotection sides; a deciding section deciding which of the working andprotection sides is selected by comparing the totaled point informationwith each other; and a main device side working/protection switchingcontrol section controlling switching between the working and protectionsides for the main device according to a deciding result of the decidingsection, and notifying each expansion device of a switching instructionsimilar to that for the main device.
 2. An optical transmission systemaccording to claim 1, wherein the point information includes a numericalvalue allocated according to a degree of a trouble indicated by theintegrated trouble information so that the deciding section selects sideof a good degree of a trouble between the working and protection sides.3. An optical transmission system according to claim 1, wherein the maindevice side working/protection switching control section notifies eachexpansion device of the switching instruction by using an overheadportion of an optical communication frame transmitted through at leastone of the plurality of optical lines for connecting themultiplexing/demultiplexing section of the protection side of the maindevice and the multiplexing/demultiplexing section of the protectionside of each expansion device.
 4. An optical transmission systemaccording to claim 1, wherein the expansion device sideworking/protection switching control section controls switching of theexpansion device itself to the working side when the switchinginstruction cannot be received from the main device due to a trouble ofthe optical lines.
 5. An optical transmission system according to claim1, wherein the integrating section, if all the degrees of troubles ofthe plurality of optical lines for both the working and protection sidesin one of the plurality of expansion devices are not good, excludes thetrouble information of the expansion device from an integration target.